The present invention relates generally to electromagnetic rail guns (EMGs), and in particular to controlling and guiding current pulses that are generated in rotating machines such as synchronous generators intended to power electromagnetic rail guns and, thereby, to improve the efficiency and performance of the EMGs.
According to Pratap et al. (S. B. Pratap, J. P. Kajs, W. A. Walls, W. F. Weldon, and J. R. Kitzmiller, "A Study of Operating Modes for Compulsator Based EM Launcher Systems", IEEE Transactions On Magnetics 33 (no. 1), 495 (1997), which is expressly incorporated by reference herein), EMGs built and tested up until 1998 were single phase systems. Several difficulties, including the upper limit on the rotational speed of the rotor, were encountered in cases where multi-megajoule output was required and caused attention to be focused on multi-polar/multi-phase systems.
One such multi-polar/multi-phase system 10 is shown schematically in FIG. 1. The rotating field coil 20, which is driven by external means, is first magnetized by the current that results from the discharge of the capacitor 12. Voltages are induced in the stator coils P1, P2, and P3 due to the changing magnetic flux through them, and when sufficient voltages are generated, a current flows through the field coil 20 ("self excitation" of the field coil) and, when switched, through the load 14 (the two rails of the EMG), all via the rectifying system 16 to accelerate the armature along the rails. Numeral 21 is the field initiation module.
In this three-phase, two rail system, a collection of rectifiers and switches 16 are used to provide relatively smooth acceleration to the projectile. The current through the rails of the multi-phase staged discharge of the EMG of FIG. 1 is shown in FIG. 2. The force on the projectile, applied by the sliding armature, is given by F=(1/2)L'I.sup.2, wherein L' is the inductive gradient along the rails and I is the current flowing through the armature. Because the force is proportional to I.sup.2, alternating current (ac) may be used to accelerate the projectile; however, the unsmooth acceleration, as well as other problems associated with the use of ac, as described in Pratap et al., makes ac undesirable. The acceleration along the rails (as given by Newton's second law) is: a=F/m, where a is the acceleration, F is the force, and m is the combined mass of the projectile, armature, and sabot.